Reduction of NiO Platelets in a NiO/ZrO ₂ (CaO) Directional Composite

Oriented lamellar eutectic composites of NiO and ZrO 2 (CaO) platelets were reduced in CO 2 /CO gaseous atmospheres to form metallic Ni between the zirconia plates. The relatively rapid longitudinal reduction of NiO is described by a local cell electrochemical model whereby oxide ions are conducted from the Ni/NiO internal reaction front to the external surface through the zirconia electrolyte, while electrons are passed through the Ni product. Both the product morphologies and the reaction kinetics are consistent with the model. Apparent “lateral’reduction of NiO platelets indeed corresponds to longitudinal reduction for a platelet inclined to the external surface. Some plastic deformation of the product zone permits partial accommodation of the volume change upon reduction of NiO to Ni.